1 . Field of the Invention
The present invention relates generally to aircraft guidance and control with differential global navigation satellite systems (DGNSSs), and in particular to a DGNSS-based system and method for optimizing crop dusting with dry materials.
2 . Description of the Related Art
GNSS guidance and control are widely used for vehicle and personal navigation and a variety of other uses involving precision location in geodesic reference systems. GNSS, which includes the Global Positioning System (GPS) and other satellite-based positioning systems, can achieve greater accuracy with known correction techniques, including a number of commercial satellite based augmentation systems (SBASs).
Aircraft are often used to spray and dust croplands, forests and other land areas with chemicals, fertilizers, seeds, water, fire suppressants and other materials. These materials may be liquid or solid. An important objective in spraying and dusting crops and in aerial firefighting is even coverage without gaps or overlaps. Another major objective is avoiding exclusion areas, which can be located internally within a field or forest being treated, or externally beyond its borders. Dry materials are typically dropped from fixed and rotary wing aircraft using spreaders. These spreaders clamp to a gate box at the base of a hopper located inside of the fuselage. As the gate box is opened, material flows from the hopper into the spreader and is pushed out behind the aircraft by air passing through the spreader. Historically these systems had to be operated manually, but methods now exist that will allow these systems to operate electronically and/or hydraulically via switches in the cockpit. However, precise distribution control presents challenges with existing equipment.
Aircraft can use venturi spreaders to distribute seed, dusting material, and other chemicals. Venturi spreaders clamp to a gate box at the base of a hopper. As the adjustable door of the gate box opens, seeds, chemicals and other materials from the hopper fall into the venturi spreader and airflow through the spreader distributes it. The amount the door is opened determines the material flow rate. Optional agitators to help material exit the hopper and gate box assembly can also be included.
Ideally the material being dropped from the aircraft will entirely cover the property being targeted while avoiding exclusion areas. However, factors such as the altitude of the aircraft, the ground speed of the aircraft, temperature, humidity, moisture content of the material and ambient wind speed and direction can affect the results. Flying too high or too low can distort the swath of the spread and result in misapplication of the material. Guidance systems, such as DGNSS, combined with electronic controllers for the spreading equipment, can optimize crop dusting.
Aerial photography, videography, surveying and telemetry procedures commonly require accurate navigation and aircraft locating equipment and methods in order to achieve optimum results. Flight guidance has also been automated with autopilots, automatic landing systems, navionics and other equipment. Such procedures can benefit from accurate GNSS-based control systems and methods.
DGNSS can utilize satellite based augmentation systems (SBAS), including the Wide Area Augmentation System (WAAS) (U.S.), and similar systems such as EGNOS (European Union) and MSAS (Japan). When accomplished with two or more antennas at a fixed spacing, an angular rotation may be computed using the position differences. In an exemplary embodiment, two antennas placed in the horizontal plane may be employed to compute a heading (rotation about a vertical axis) from a position displacement. Heading information, combined with position, provides the feedback information desired for a proper control of the vehicle direction.
Another benefit achieved by incorporating a GNSS-based heading sensor is the elimination or reduction of drift and biases resultant from a gyro-only or other inertial sensor approach. Yet another advantage is that heading may be computed while movable equipment is stopped or moving slowly, which is not possible in a single-antenna, GNSS-based approach that requires a velocity vector to derive a heading. Yet another advantage of incorporating a GNSS-based heading sensor is independence from a host vehicle's sensors or additional external sensors. Thus, such a system is readily maintained as equipment-independent and may be moved from one vehicle to another with minimal effort.
An example of a GNSS is the Global Positioning System (GPS) established by the United States government, which employs a constellation of 24 or more satellites in well-defined orbits at an altitude of approximately 26,500 km. These satellites continuously transmit microwave L-band radio signals in two frequency bands, centered at 1575.42 MHz and 1227.6 MHz, denoted as L1 and L2 respectively. These signals include timing patterns relative to the satellite's onboard precision clock (which is kept synchronized by a ground station) as well as a navigation message giving the precise orbital positions of the satellites, an ionosphere model and other useful information. GPS receivers process the radio signals, computing ranges to the GPS satellites, and by triangulating these ranges, the GPS receiver determines its position and its internal clock error.
In standalone GPS systems that determine a receiver's antenna position coordinates without reference to a nearby reference receiver, the process of position determination is subject to errors from a number of sources. These include errors in the GPS satellite's clock reference, the location of the orbiting satellite, ionosphere-induced propagation delay errors, and troposphere refraction errors.
To overcome these positioning errors of standalone GPS systems, GPS applications have been improved and enhanced by employing a broader array of satellites such as GNSS and WAAS. For example, see commonly assigned U.S. Pat. No. 6,469,663 to Whitehead et al. titled Method and System for GPS and WAAS Carrier Phase Measurements for Relative Positioning, dated Oct. 22, 2002 , the disclosures of which are incorporated by reference herein in their entirety. Additionally, multiple receiver DGPS has been enhanced by utilizing a single receiver to perform differential corrections. For example, see commonly assigned U.S. Pat. No. 6,397,147 to Whitehead titled Relative GPS Positioning Using A Single GPS Receiver With Internally Generated Differential Correction Terms, dated May 28, 2002 , the disclosures of which are incorporated by reference herein in their entirety.
Heretofore there has not been available a GNSS system and method for guiding aircraft to optimize various procedures, including the spreading of solid material accurately on a predetermined area within relatively precise boundaries while avoiding exclusion areas with the advantages and features of the present invention.